Photodiodes are the most commonly used photodetectors in use today. Presently, they are used in any variety of applications and are rapidly being incorporated into numerous additional applications. Generally, photodiodes offer a compact, rugged, low cost alternative to photomultipliers or similar devices.
Currently, photodiodes are manufactured from a number of materials, each material offering sensitivity within a defined range of the electromagnetic spectrum. For example, as shown in FIG. 1, Silicon-based photodiodes and photodetectors typically produce significant photocurrents when irradiated with a signal having a wavelength from about 180 nm to about 1100 nm. In contrast, as shown in FIG. 2, Germanium-based photodiodes produce significant photocurrents when irradiated with a signal having a wavelength from about 800 nm to about 1800 nm.
Presently, various applications utilize both Silicon-based photodiodes and Germanium-based photodiodes to measure optical signals having broad spectral characteristics (e.g. from about 180 nm to about 1800 nm). As shown in FIGS. 3-5, multiple approaches have been utilized in the past to construct a device or system which incorporates both Silicon-based photodiodes and Germanium-based photodiodes. For example, as shown in FIG. 3, prior art systems included a split light approach which included a wavelength-dependent mirror or filter to separate the incident light at a desired wavelength. While this approach proved somewhat useful in the past, a number of shortcomings have been identified. For example, as shown in FIG. 4, a pronounced wavelength dependent responsivity gap is present at the point at which the mirror transitions from absorbing to transmitting an incident broad spectrum light.
In response, as shown in FIG. 5, an alternate prior art approach was developed which utilized a multiple layer or sandwich detector, wherein the photodiode comprises a Silicon-based detector applied to the body of a Germanium-based detector. Again, as shown in FIG. 6, a pronounced wavelength dependent responsivity gap is present at the point at which the Silicon-based detector transitions from absorbing to transmitting an incident broad spectrum light using a sandwich detector approach.
Further, the responsivity of these devices varies depending on the wavelength of the incident signal. For example, while Silicon-based photodetectors are capable of detecting signals having a wavelength from about 180 nm to 1100 nm, the highest responsivity is from about 850 nm to about 1000 nm. As such, the measurement of broad spectral ranges typically requires multiple photodetectors each manufactured using photodiodes manufactured from different materials. As such, systems incorporating multiple photodetectors manufactured from various materials may be large and unnecessarily complex.
Thus, there is an ongoing need for a multi-junction detector device capable of detecting an incident signal with high responsivity at a variety of wavelengths with very few if any spectral gaps or discontinuities, thereby offering smooth, continuous spectral measurements.